Method for providing multicast and/or broadcast services to user terminals

ABSTRACT

The invention relates to a method for providing multicast and/or broadcast services to user terminals ( 8, 9 ) via a cellular network ( 2, 5 ). In order to increase the efficiency of multicast or broadcast transmissions, it is proposed that each of said user terminals ( 8, 9 ) willing to receive content data of at least one multicast and/or broadcast service enters at least once for a pre-determined time a state in which it is capable of receiving content data of said multicast and/or broadcast service. The invention equally relates to a corresponding user terminal, to a corresponding cellular network and to a corresponding mobile radio system.

FIELD OF THE INVENTION

The invention relates to a method for providing multicast and/orbroadcast services to user terminals via a cellular network. Theinvention equally relates to such a user terminal, to such a cellularnetwork, to a network element of a cellular network, and to a mobileradio system comprising such a user terminal and such a cellularnetwork.

BACKGROUND OF THE INVENTION

Broadcast and Multicast are methods for transmitting data-grams from asingle source to several destinations, i.e. as point-to-multipointtransmission.

As mentioned in the technical specification 3GPP TS 22.146 V5.0.0(2001-10): “Multimedia Broadcast/Multicast Service; Stage 1 (Release5)”, currently two such services are specified for cellular networks,the cell broadcast service (CBS) and the internet protocol (IP)multicast service.

The cell broadcast service enables a transmission of low bit-rate datato all subscribers in a set of given radio cells of a cellular networkover a shared broadcast channel.

The transmission of content data for IP multicast services, providede.g. by an internet service provider, to user terminals via a radiointerface can currently be supported by GPRS (general packet radiosystem) based cellular networks. It is required, however, that apoint-to-point PDP (packet data protocol) context is set up betweenevery user terminal and a network element of the GPRS network, i.e. theGGSN (Gateway GPRS support node), and every user terminal receiving a IPmulticast transmission occupies a separate radio channel. Several radiochannels thus deliver the same content in a point-to-point way through aGPRS system.

For UMTS, 3GPP (3rd generation partnership project) is developing newservices for multicast and broadcast in UMTS. In the above mentionedtechnical specification 22.146, 3GPP provides for example a stage onedescription of broadcast and multicast services for UMTS. One desirablefeature for new multicast services is for example to enable thetransmission of an IP-multicast service content via a radio accessnetwork of a UMTS system to several user terminals with a shared radiochannel. For both, new broadcast and new multicast services, a procedurefor activating a broadcast or multicast session on the radio interfacestill has to be provided.

From an IP multicast content source point of view, the handling of amulticast transmission by a radio access network should be similar toIP-multicast, in order to avoid a conflict with the IETF IP-Multicastingstandards.

In the RFC (Request for Comments) 2236: “Internet Group ManagementProtocol, Version 2”, of November 1997, it is specified for example thatmulticast routers use IGMP (Internet Group Management Protocol) to learnwhich groups have members on each of their attached physical networks.It is requested that a multicast router keeps a list of multicast groupmemberships for each attached network, and a timer for each membership.The expression ‘Multicast group memberships’ means the presence of atleast one member of a multicast group on a given attached network, not alist of all of the members.

SUMMARY OF THE INVENTION

It is an object of the invention to enable an efficient delivery ofmulticast and/or broadcast services to mobile users by a cellularnetwork. It is in particular an object of the invention to enable anactivation of multicast or broadcast sessions only in such radio cellsof the cellular network, in which the number of likely receivers exceedsa predetermined value.

In order to reach the objects of the invention, a method for providingmulticast and/or broadcast services to user terminals via a cellularnetwork is proposed, in which method each of these user terminals whichis willing to receive content data of at least one multicast and/orbroadcast service enters at least once for a predetermined time a statein which it is capable of receiving content data of said multicastand/or broadcast service.

The state in which a user terminal willing to receive content data of aspecific multicast or broadcast service is in addition capable ofreceiving such content data will also be referred to as READY state. Inthe state in which a user terminal is willing to receive content data ofa specific multicast or broadcast service, it is in contrast not capablewithout any further action of receiving such content data will bereferred to as STANDBY state.

The object is equally reached with a user terminal, with a cellularnetwork, with a network element for a cellular network, and with acommunication system comprising means for realizing the proposed method.

The invention proceeds from the idea that if a user terminal enters fora time a READY state when it is willing to receive content data of amulticast and/or broadcast service, it can be provided with such contentwithout any further action being required for the transmission duringthis time, thus making the delivery of a service more efficient.

In a preferred embodiment of a first approach for further developing theinvention, at least some of the user terminals willing to receivecontent data of at least one multicast and/or broadcast service transmita corresponding indication to the cellular network, which indication canprovide the network in particular with an information on which multicastand/or broadcast services the respective user terminal is willing toreceive. The indication can consist for example of an indication that arespective user terminal joins a group of user terminals willing toreceive at least one specific multicast and/or broadcast service. Asconsequence, the cellular network can determine whether there is asufficient number of likely receivers in a specific cell for thedelivery of multicast and/or broadcast services.

Advantageously, the cellular network has moreover knowledge about thetime during which a user terminal remains in a READY state. In thiscase, the cellular network does not only know how many likely receiversthere are for a service, but also many of them are currently in a READYstate and for how long. The cellular network does not have aninformation on the exact location of user terminals in the STANDBYstate. With the knowledge about the time during which each user terminalremains in a READY state, the cellular network can therefore determinewith an increased certitude the number of likely receivers in a specificcell for the delivery of multicast and/or broadcast services.

The time during which a respective user equipment remains in a READYstate can be fixed for all user terminals and known at the network. Inthis case, the network knows already only with the indication of a userterminal that it is willing to receive content data for a multicastand/or broadcast service, for how long this user terminal will stay inthe READY state and thus be able to receive content data.

Alternatively, at least some of the user terminals willing to receivecontent data of at least one multicast and/or broadcast service transmitin addition an indication to the cellular network for how long they willremain in the READY state. The indication of a time for how long a userterminal will be in the READY state could also be transmitted by itselfto the cellular network. This is of particular interest for a laterpoint of time, at which a user terminal has already switched from theREADY state to the STANDBY state, and then returns to the READY state,e.g. because of some other transmission.

The first approach of the invention enables a network element of thecellular network in particular to immediately respond to a polling by amulticast and/or broadcast router wishing to provide content data for aservice, since it knows for how long how many user terminals willing toreceive such content data will be in the READY state.

In a preferred embodiment of a second approach for further developingthe invention, a network element of the cellular network transmits apaging message when a multicast/broadcast router starts to delivercontent data for a specific multicast or broadcast service. To thispaging message, each user terminal, which is willing to receive contentdata of this specific multicast or broadcast service but for which saidpredetermined time has passed, can respond, in case it actually receivesthe paging message.

This second approach is based on the idea that if user terminals in aSTANDBY state are paged by the cellular network when a multicast orbroadcast service is to be provided, the number of responses by theseterminals indicates to the cellular network whether there is asufficient number of likely receivers for the delivery of multicastand/or broadcast services.

It is an advantage of the second approach of the invention that anevaluation of likely receivers is also possible, after the terminals inthis cell have turned to the STANDBY state. The evaluation can beperformed separately for each radio cell of the cellular network.

Also in the second approach, each user terminal willing to receivecontent data of at least one multicast and/or broadcast service cantransmit a corresponding indication to the cellular network. Thisindication can provide the cellular network with additional informationfor paging.

Both approaches thus provide the cellular network with a reliableinformation on a minimum number of user terminals which are currentlyavailable for receiving content data of a broadcast or multicastservice.

It is a further advantage of both approaches of the invention, that fromthe content source point of view, the handling can be made similar tothe IETF specified IP multicasting.

The invention can be employed in particular, though not exclusively, forUMTS.

Further, the invention can be employed in particular for supporting IPmulticasting via the radio interface of a cellular network, but also forother types of multicast services or for broadcast services.

Preferred embodiments of the invention are included in the subclaims.

BRIEF DESCRIPTION OF THE FIGURES

In the following, the invention is explained in more detail withreference to a drawing, of which the only FIGURE shows an environment inwhich an embodiment the invention can be employed.

DETAILED DESCRIPTION OF THE INVENTION

The only FIGURE shows selected elements of a communication system thatare involved in embodiments of the invention according to the first orthe second approach, which both support IP-multicasting via a cellularnetwork to user terminals. The system comprises the internet, a PLMN ascellular network providing UMTS, and user terminals.

In the FIGURE, the internet 1 is connected to a GGSN 3 of a core network2 of the PLMN. The GGSN 3 is further connected via an SGSN (switchingGPRS support node) 4 of said core network 2 to at least one RNC 6 of anUTRAN 5 of the PLMN. Within the UTRAN 5, the RNC 6 has a controllingaccess to at least one node B 7. The node B 7, finally, can provide viaa radio interface a connection to user terminals 8, 9 which are locatedin a radio cell defining the coverage area of the node B 7.

A user terminal 8, 9 that is subscribing a specific multicast serviceprovided by an internet service provider and that is currently willingto receive this service informs the cellular network that it joins amulticast group defined for receiving this specific service. The mobilejoins this group using a specific multicast PDP context or a normal PDPcontext which is transmitted to the cellular network.

After joining the group, the user terminal 8, 9 remains in a READY statefor a predetermined time, i.e. until a timer T1 provided in the userterminal 8, 9 runs up. Then, the user terminal 8, 9 enters a STANDBYstate. The READY state will be entered again for the predetermined timewhen a PDP context is activated for a data transmission. Only in theREADY state, a user terminal 8, 9 is able to receive multicast orbroadcast transmissions without first having to activate a PDP context.

A differentiation between a STANDBY state and a READY state has alreadybeen described for GPRS, e.g in the technical specification 3GPP TS23.060 V3.6.0 (2001-01): “General Packet Radio Service (GPRS); Servicedescription; Stage 2 (Release 1999)”. In the STANDBY state, pagingmessages for data or signaling information transfers may be received. Itis necessary, however, to activate a PDP context before data can betransmitted or received. Such an activation can be initiated by the userterminal e.g. upon a paging message. For user terminals in the READYstate, the network transmits no GPRS paging messages, since the userterminal is already able in this state to send and receive PDP PDUs(protocol data units) employed for transmitting content data. The READYstate is supervised by a timer. A user terminal moves from the READYstate to the STANDBY state when the timer expires.

The timer T1 of the user terminals 8, 9 depicted in the FIGURE may beidentical with the timer currently defined for GPRS. Alternatively, itmay be a new timer introduced specifically for multicast services.

Within the cellular network, the information that a user terminal 8, 9has joined a multicast group is received by the node B 7 and forwardedvia the RNC 6 and the SGSN 4 to the GGSN 3. The GGSN 3 thus knows whichuser terminals 8, 9 have joined a multicast group for a specificservice.

In the embodiment according to the first approach, a user terminal 8joining a multicast group transmits at the same time a timer value MC1,which indicates for how long this user terminal 8 will be able toreceive an IP multicast transmission for this multicast group, i.e. forhow long it will remain in the READY state.

Equally, another user terminal 9 may join the same multicast group andtransmit a corresponding timer value MC2.

The timer values MC1, MC2 are forwarded together with the indicationthat a user terminal 8, 9 wishes to join a specific multicast group tothe GGSN 3. The RNC 6 and the SGSN 4 also know the user terminals 8, 9that are still able to receive multicast messages after having joined acorresponding multicast group.

In case an IP-multicast router wants to transmit content data for aspecific IP multicast service received from an internet serviceprovider, it first performs a polling with the GGSN 3. Only if the GGSN3 responds to the polling, the content data will actually betransmitted. Since the GGSN 3 knows the timer values MC1, MC2 of alluser terminals 8, 9 that have joined a specific multicast group, it isat any time aware of whether there are user terminals 8, 9 in itscoverage area, which are still in the READY state. As long as there aresuch user terminals in the READY state, it can respond to a polling by amulticast router.

In the embodiment according to the second approach, a determination ofuser terminals 8, 9 which have joined a specific multicast group and arestill available for receiving content for this service is carried out bythe RNC 6.

When an IP multicast router starts to deliver content data for aspecific multicast service, the GGSN 3 forwards the content data via theSGSN 4 to the RNC 6. The RNC 6 shall activate a multicast session inthose cells for which it controls the radio resources, in which thereare user terminals 8, 9 that have joined the corresponding multicastgroup.

User terminals 8, 9 that are in the READY state simply receive a startmessage from the RNC 6 informing them about the start of a multicastsession.

The RNC 6 is not aware, however, whether a user terminals 8, 9 in theSTANDBY state, which have joined the respective multicast group, isstill located in a radio cell supplied by the RNC 6. Therefore, the userterminals 8, 9 in the STANDBY state are first paged by the RNC 6, inorder to enable the RNC 6 to determine in which radio cell theycurrently are.

In the presented embodiment, the employed paging is a special paging formulticast services. It contains specific multicast indicators, morespecifically a multicast group indication, a multicast channelindication, and possibly some other information. The number of bits thatcan be used on the GPRS paging channel is limited. For this reason, allindicators are defined in a shortened form. Because the paging normallyserves more than one user terminal, however, the paging message can bee.g. 2 to 3 times larger than the normal paging to a single userterminal.

All user terminals 8, 9 that are in the coverage area of the RNC 6 andthat have joined the multicast group indicated in the paging message canrespond to the paging after a random delay. This random delay ensuresthat collisions between a large number of simultaneous responses areavoided. The multicast channel indication in the paging messageindicates to the user terminal 8, 9 which radio channel is to beemployed for the transmission of content data for the service via theradio interface.

In the RNC 6, a number is defined which corresponds to a sufficientnumber of responses to a paging message. This number may for instance be3, but it may also be lower or higher. As soon as the RNC 6 has receiveda number of responses which is equal to the predetermined number, theRNC 6 transmits a “paging finished” message on the paging channel. As aresult, the user terminals 8, 9 which are still waiting to send theirpaging response due to the respective random delay, will refrain fromsending a response. This function is of particular importance in largescale applications, in which there may be hundreds of user terminals 8,9 which have joined a specific multicast group in a single radio cell.

When the RNC 6 receives only one or two multicast paging responses froma radio cell, or in general terms less responses than the predeterminednumber, it forwards these back to the core network 2. In the corenetwork 2, a multicast service center, the GGSN 3 or the SGSN 4 can thendecide, whether point-to-point connections using the normal PDP contextmechanism should be set up to the corresponding user terminals 8, 9. Thedecision may be based on operator capacity preferences or on userpreferences given e.g. by different tariff levels.

This second approach can also be combined with the first approach. Apaging could for instance be carried out only in cases in which thereare not sufficient number of user terminals in the READY state.Alternatively, the paging could be employed as a control function alsowhen there are still enough timers active which indicate that userterminals are in a READY state.

It is to be noted that even though both approaches were described for IPmulticasting, they are equally applicable for other types of multicastand broadcast services.

1. A method, comprising: transmitting a paging message to user terminalswhen a multicast/broadcast router starts to deliver content data for aspecific multicast or broadcast service, the user terminals configuredto enter a state at least once for a predetermined time in which theterminals are configured to receive content data of at least one of amulticast or a broadcast service; and receiving a response from at leastsome user terminals, wherein the response comprises a time indicatinghow long the user terminals will remain in said state in which they areconfigured to receive the content data of said at least one of themulticast or the broadcast service in a cellular network.
 2. The methodaccording to claim 1, further comprising: receiving an indication fromat least some user terminals, the indication indicating that a userterminal comprises a willingness to receive the content data of at leastone of a multicast service and a broadcast service.
 3. The methodaccording to claim 2, wherein the receiving the indication comprisesreceiving the indication using a dedicated packet data protocol contextfor indicating that a user terminal comprises a willingness to receivethe content data of the at least one of the multicast or the broadcastservice.
 4. The method according to claim 2, wherein the receiving theindication comprises receiving the indication that a user terminalcomprises a willingness to receive the content data of the at least oneof the multicast or the broadcast service by a network element of saidcellular network, the method, further comprising: when said networkelement receives a polling from the multicast/broadcast router whichintends to transmit the content data for the specific multicast or thespecific broadcast service, responding to said polling when there areuser terminals that have indicated that they comprise a willingness toreceive the content data of said specific multicast or broadcastservice, wherein said predetermined time in which the user terminals areconfigured to receive the content data of said at least one of themulticast or the broadcast service has not passed.
 5. The methodaccording to claim 1, wherein the receiving the indication comprisesreceiving the response using a dedicated packet data protocol contextfor indicating said time that a user terminal is configured to remain insaid state in which it is configured to receive the content data of saidat least one of the multicast or the broadcast service.
 6. The methodaccording to claim 1, wherein the receiving the response comprisesreceiving said response indicating a time for how long a user terminalis configured to remain in said state in which it is configured toreceive said at least one of the multicast or the broadcast service at anetwork element of said cellular network, the method, furthercomprising: when the network element receives a polling from themulticast/broadcast router which intends to transmit the content datafor the specific multicast or the specific broadcast service, respondingto polling when there are user terminals of which said indicated timehas not passed.
 7. The method according to claim 1, wherein thereceiving the response from a user terminal comprises receiving theresponse to the paging message upon expiration of the predeterminedtime.
 8. The method according to claim 1, further comprising: receivingthe response from at least some user terminal, wherein the response isconfigured to show a willingness to receive the content data of the atleast one of the multicast or the broadcast service by the cellularnetwork.
 9. The method according to claim 1, further comprising:transmitting a start message from a network element to the userterminals, when the multicast/broadcast router starts to deliver thecontent data for the specific multicast or broadcast service to saidnetwork element of said cellular network, wherein the start message isconfigured to indicate that a multicast or broadcast session isstarting, and wherein the user terminals are configured to receive thecontent data of the at least one of the multicast or the broadcastservice.
 10. The method according to claim 1, wherein the transmittingthe paging message comprises transmitting a dedicated paging messageconfigured for said at least one of the multicast or the broadcastservice.
 11. The method according to claim 1, wherein the transmittingthe paging message comprises transmitting the paging message comprisingat least one of a multicast or broadcast group indication configured toindicate said specific multicast or broadcast service for which thecontent data is to be transmitted, and a multicast or broadcast channelindication configured to indicate a radio channel configured to transmitsaid content data via a radio interface to said user terminals.
 12. Themethod according to claim 1, wherein the receiving the responsecomprises receiving a response to the paging message from a userterminal, which indicated that it comprises a willingness to receive thecontent data of said specific multicast or broadcast service and whichreceives the paging message, but for which said predetermined time haspassed, after a random delay.
 13. The method according to claim 1,further comprising: transmitting an indication that a paging isterminated after a network element of the cellular network has receivedat least a predetermined number of responses to said paging message,wherein the user terminals, which have not yet responded to said pagingmessage, are configured not to respond after receiving said indicationthat said paging is terminated.
 14. The method according to claim 1,further comprising: transmitting the content data for the specificmulticast or broadcast service delivered by the multicast/broadcastrouter in a specific radio cell without a further decision of atransmission in the cellular network, when a network element of thecellular network receives at least a predetermined number of responsesfrom the user terminals located in the specific radio cell; anddetermining in the cellular network whether a point-to-point connectionis to be established to the user terminals in the specific radio cellwhich responded to the paging message, when the network element of thecellular network receives less than the predetermined number ofresponses from the user terminals located in the specific radio cell forthe paging message.
 15. An apparatus, comprising: transmission means fortransmitting a paging message to user terminals when amulticast/broadcast router starts to deliver content data for a specificmulticast or broadcast service, the user terminals being configured toenter a state at least once for a predetermined time in which they areconfigured to receive content data of at least one of a multicast or abroadcast service and to respond to the paging message; and receivingmeans for receiving at least one response from at least some of the userterminals configured to receive the content data of the at least one ofthe multicast or the broadcast service, wherein the at least oneresponse comprises a time indicating how long the user terminals isconfigured to remain in said state in which they are configured toreceive the content data of said at least one of the multicast or thebroadcast service in a cellular network.
 16. An apparatus, comprising: anetwork element, comprising a transmitter configured to transmit apaging message to user terminals when a multicast/broadcast routerstarts to deliver content data for a specific multicast or broadcastservice, the user terminals being configured to enter a state at leastonce for a predetermined time in which they are configured to receivecontent data of at least one of a multicast or a broadcast service andto respond to the paging message; and a receiver configured to receiveat least one response from at least some of the user terminalsconfigured to receive the content data of the at least one of themulticast or the broadcast service, wherein the at least one responsecomprises a time indicating how long the user terminals is configured toremain in said state in which they are configured to receive the contentdata of said at least one of the multicast or the broadcast service in acellular network.
 17. A system, comprising: an apparatus, comprising anetwork element, comprising a transmitter configured to transmit apaging message to user terminals when a multicast/broadcast routerstarts to deliver content data for a specific multicast or broadcastservice, the user terminals being configured to enter a state at leastonce for a predetermined time in which the terminals are configured toreceive content data of at least one of a multicast or a broadcastservice and to respond to the paging message; and a receiver configuredto receive at least one response from at least some of the userterminals configured to receive the content data of the at least one ofthe multicast or the broadcast service, wherein the at least oneresponse comprises a time indicating how long the user terminals isconfigured to remain in said state in which they are configured toreceive the content data of said at least one of the multicast or thebroadcast service in a cellular network.
 18. An apparatus, comprising: atransmitter configured to transmit a paging message to user terminalswhen a multicast/broadcast router starts to deliver content data for aspecific multicast or broadcast service, the user terminals beingconfigured to enter a state at least once for a predetermined time inwhich they are configured to receive content data of at least one of amulticast or a broadcast service and to respond to the paging message;and a receiver configured to receive at least one response from at leastsome of the user terminals configured to receive the content data of theat least one of the multicast or the broadcast service, wherein the atleast one indication comprises a time indicating how long the userterminals is configured to remain in said state in which they areconfigured to receive the content data of said at least one of themulticast or the broadcast service in a cellular network.
 19. Theapparatus according to claim 18, wherein said apparatus comprises aradio network controller of a universal mobile telecommunicationservices cellular network.